In a release of toxic chemicals into an urban or indoor environment, a wide range of compounds will be dispersed in addition to the principal toxin. These compounds, often referred to as “chemical attribution signature” (CAS) compounds, are derived from the synthesis and degradation of the toxin mixture, thus, they are highly indicative of the synthetic route, stabilization, storage, and methods of release. CAS compounds may have significant forensic value, provided they may be effectively collected at the event site.
For example, during the release of a chemical warfare agent (CWA) as an act of terrorism, there is a potential for a significant number of casualties from exposure to one or more toxins in the CWA. Such casualties may occur by inhalation or by dermal contact with aerosols or contaminated surfaces. In the aftermath of a CWA release, treatment of the victims, and decontamination and re-entry of the affected area will be high recovery priorities. Another activity of high priority will be fast and accurate identification of the perpetrators.
The identification of the CWA is the first and most important objective, since this dictates treatment of the victims and provides guidance for the amount of time an affected area will remain toxic due to residual agent. CWA identification is expected to be straightforward because analytical approaches are well developed. However, identification of the agent alone is not likely to provide substantial forensic information. A more detailed analysis having greater forensic value may be gained by identifying synthetic byproduct compounds that may be present in the agent. Synthetic byproduct compounds are indicative of a synthetic route that was used to synthesize the CWA, and may also contain information on how the agent was stored, stabilized, and released. Because the synthetic byproducts present in the CWAs are unique to synthetic routes used in their formation, these compounds may be used as CAS compounds.
The characterization of CAS compounds on fixed surfaces may be analytically challenging for several reasons. The chemical background in an anthropogenic environment includes a large number of compounds that may be present in high concentrations. For example, virtually any polymeric material will contain a large quantity of plasticizers and solvents, which will produce analytical responses that may be distinguished from those of the CAS compounds. The CAS compounds that are of highest value for identifying synthetic approaches will frequently be present at trace concentrations. These compounds are not formed intentionally, and their concentrations may have been reduced by purification steps used in synthesis. The concentrations of some of the toxins and the CAS compounds may decrease quickly after release, on account of volatilization and loss to the atmosphere, diffusion into a bulk solid, and/or degradation reactions. The CAS compounds may undergo degradation by hydrolysis, photolysis, oxidation, or condensation with other compounds in the chemical environment. Hydrolysis and oxidation reactions may be enhanced by treatment with decontamination solutions during recovery efforts. These degradation reactions may result in changes to the chemical nature of the CAS compounds that drives the need for effective sampling of exposed surfaces.
A method of analyzing organic compounds, such as phosphoryl compounds, sulfide compounds, and amine compounds, may be performed without sample preparation by bombarding surfaces with energetic molecules. More specifically, surface-adsorbed compounds are sputtered into the gas phase where they may be detected using mass spectrometry (MS). The drawback to this method is that it requires acquisition of a sample of the solid surface.
More recently, new approaches have emerged that enable direct interrogation of surfaces using a mass spectrometer. One such approach is desorption electrospray ionization (DESI) mass spectrometry, which utilizes energetic droplets to impact contaminated surfaces. The droplets pick up surface contaminants that are then analyzed, and the technique has recently been demonstrated for analysis of chemical warfare agents. Another approach, referred to as “direct analysis in real time” (DART), utilizes an energetic noble gas plasma to remove surface contaminants that are then analyzed using mass spectrometry. Although these techniques enable on-site analysis, they are expensive, difficult to transport, and hence are not viable options for most law enforcement organizations.
CWA and associated CAS compounds may contact multiple fixed surfaces, and cannot be readily sampled using conventional approaches involving removal and transport to a forensic laboratory for analysis. There is a need for facile, rapid collection of samples containing chemical warfare agent (CWA) attribution signatures after a CWA release.